Operating and controlling positioning of multiple objects when the objects change position and orientation individually is a common challenge in everyday life. Specifically complex is this when one object is to be loaded or unloaded to/from a second independently moving object. This is typically seen in offshore cargo loading/unloading scenarios, but can easily be found elsewhere in a wide variety of scenarios such as in space environments when spaceships are to be connected, or in a forest environment when a moving tree-cutting machine loads timber to an individually moving lorry.
Traditionally the task of loading and unloading is handled by skilled operators of crane or other connection system and the use of different warning and measurement systems.
Solutions to the task of loading and unloading in an offshore environment where a boat with a crane is moving under influence of waves, and heave compensation is performed to have a load stabilized even if the crane construction is moving is known to a person skilled in the art.
U.S. Pat. No. 6,505,574 B1 discusses solutions to the problem where a method and system are provided for reducing sea state induced vertical velocity of the crane's suspended load.
U.S. Pat. No. 5,943,476 discusses in some aspects the measurement of the orientation of an object related to positioning robotic end effectors.
Common to most available advanced systems is that they present solutions related to loading and unloading when the crane/operator itself is under influence of motion, and where the task is to compensate and keep the absolute motion of the cargo as stable as possible, or where a system is calculating the orientation of an object for the purpose of further handling by the system.
Standards and specifications in the shipping transport industry put constraints on maximum allowable load weights for loading/unloading under rough sea conditions, and by that increasing the cost factors of loading and unloading cargo between/to/from seagoing vessels. Standards also require that the allowed lifting capacity is reduced based on maximum significant wave-height, making lifting operations less effective when maximum significant wave-height increases.
Problems arise when cargo is to be loaded or unloaded in unstable conditions, such as in turbulent sea states (large waves) and where a loading device mounted on a fixed or floating vehicle, i.e. a crane mounted on an oil rig, is potentially moving independent of the target plane, such as the loading deck on a supply ship moving independently of the crane, and the cargo may be prone to swing out of focus of the guiding systems. These situations, together, partially together or individually, create difficult working conditions for the crane operators, and together with low weight tolerances due to limitations to human capabilities, standards and regulations, these factors increase the amount of work and complexity of loading and unloading cargo.
There is a need for an improved system to provide automatic compensation for the distance variation between the cargo and the plane of which it is loaded or unloaded irrelevant of the movement of the plane itself or the vehicle holding/lifting the cargo, such as the crane mounted on a platform in a crane lifting operation.